It is known to use, as a carbon nanostructure material, fibrous nano-carbon produced generally by bringing gas containing carbon into contact with a selected catalyst metal at a temperature of about 500° C. to 1200° C. for a prescribed period of time.
Examples of methods of producing a carbon nanostructure material include an ark discharge method, laser vapor deposition method, and chemical vapor deposition method (CVD method).
In the arc discharge method, arc discharge is made to generate between positive and negative graphite electrodes to thereby vaporize graphite, and a carbon nanotube is generated in a carbon deposit condensed at the tip of the negative electrode.
The laser vapor deposition method involves steps of adding a graphite sample mixed with a metal catalyst in inert gas heated to a high temperature and irradiating the graphite sample with a laser beam to thereby produce a carbon nanostructure material.
Although a carbon nanostructure material having high crystallinity can generally be generated in the arc discharge method and laser vapor deposition method, the amount of carbon to be generated is small and it is therefore said that these methods are scarcely applied to mass-production.
The CVD method is typified by two methods including a vapor deposition substrate method in which a carbon nanostructure material layer is formed on a substrate disposed in a reaction furnace and a fluidized vapor phase method in which a catalyst metal and a carbon source are fluidized together in a high-temperature furnace to synthesize a carbon nanostructure material.
However, the vapor deposition substrate method has a difficulty in attaining mass-production because it is carried out by batch treatment. Also, the direct injection pyrolytic method is inferior in temperature uniformity and is regarded as difficult to produce a carbon nanostructure material having high crystallinity. Moreover, a method modified from the fluidized vapor phase method is known in which a fluidized layer is formed in a high-temperature furnace from a fluidizing material also functioning as a catalyst and carbon raw material is supplied to the furnace to produce a fibrous carbon nanostructure material. This method is, however, inferior in temperature uniformity in the furnace so that it is assumed that this method has a difficulty in generating a carbon nanostructure material having high crystallinity.
The importance of nanostructure materials and particularly, graphite carbon nano-fibers has sharply increased in many industrial applications and studies as to the applications of these nanostructure materials are being made. Examples of these applications include occlusion and absorption/desorption of hydrogen, occlusion and absorption/desorption of lithium, catalytic action, and absorption and occlusion of nitrogen oxides. However, these nanostructure materials still have poor industrial applicability at present. One of the reasons is that structurally uniform graphite carbon nano-fibers cannot be mass-produced.
In light of this, if graphite carbon nano-fibers superior in the high stabilities of, for example, dimension, shape, structure and purity can be mass-produced efficiently at low cost, nano-technological products making use of the characteristics of these graphite carbon nano-fibers can be supplied in a large amount at low cost.